I hear snakes... I hate snakes

This alert simply means that the level will contain significantly more snakes and cobras than anything else. Otherwise, the level in which this alert is encountered won't be any different.

One of the only other differences is that a 'snake pit' will be somewhere in the level. This pit hard to get out of without using ropes and bombs (easy with climbing gloves or jetpack). Along the sides are usually chests, crates, gems and sometimes damsels. The bottom will have four snakes/cobras and rubies. If you bomb the bottom of the snake pit, you will be rewarded with a Mattock. This holds true in both pc and Xbox Live Arcade editions of Spelunky.